1. Field of the Invention
The present invention relates to a lubricating system of an engine, and more particularly to a dry sump type or semidry sump type lubricating system of an engine which is operated while keeping an inner side of a crank chamber in a dry state.
2. Description of the Related Art
A dry sump type lubricating system of an engine corresponds to a system in which an oil tank is installed as an oil reservoir portion separately from a crank case, and a predetermined amount of oil is reserved in the oil tank. On the other hand, a semidry sump type lubricating system utilizes a lower portion of a transmission room within a crank case as the oil reservoir portion, for example, by forming a partition wall between a crank chamber and the transmission room, without installing the separate type oil tank, and reserves the oil in the oil reservoir portion. Such semidry sump type lubrication system is disclosed in Japanese Unexamined Patent Publication No. H06-288466. Comparing with the dry sump type lubricating system, since it is unnecessary for the semidry sump type lubricating system to install the separate type oil tank, it is possible to save a cost and an arranging space for the oil tank, and it is possible to achieve a compact structure of the engine.
Either of the dry sump type lubricating system and the semidry sump type lubricating system is structured such that the oil is pressure fed to each oil supply positions of the engine from the oil reservoir portion by a feed oil pump, the oil after being used for lubrication coming down to the crank case or a bottom portion of an oil pan is forcibly pumped out to the oil reservoir portion by an additional oil pump (a so-called scavenging oil pump), and an inner side of the crank chamber is always kept in a dry state. Accordingly, it is possible to do away with a friction loss caused by agitation and splashing of the oil by the crank shaft (a crank web or the like), it is possible to improve an engine output, and it is possible to pressure feed and supply the oil to each oil supply position in a stable state.
In the dry sump type lubricating system or the semidry sump type lubricating system, it is necessary to quickly discharge the oil coming back to the crank chamber during the engine operation. However, in the case of a multi-cylinder in-line engine in which plural cylinders are arranged along the crank shaft, since the crank case is partitioned into plural crank chambers by a partition wall or more corresponding to cylinders, it is required that the oil can be quickly discharged from each of the crank chambers.
Conventionally, in order to discharge the oil in each crank chamber, an oil drain port is formed in a bottom surface or a side surface of one of plural crank chambers, and a communication hole is formed in the partition wall between the crank chambers. In other words, the oil coming back to the bottom surface of each crank chamber from the crank shaft or the like is collected to one crank chamber having the oil drain port via the communication hole of the partition wall, and is discharged from one oil drain port.